電動モーター | 定義、種類、事実 | ブリタニカ

Electric motor | Definition, Types, & Facts | Britannica Ask the Chatbot Games & Quizzes History & Society Science & Tech Biographies Animals & Nature Geography & Travel Arts & Culture ProCon Money Videos electric motor Introduction Induction motors Construction of induction motors Starting characteristics Protection Wound-rotor induction motors Single-phase induction motors Capacitor induction motor Split-phase motors Shaded-pole motors Servomotors Linear induction motors Induction motors for speed and position control Synchronous motors Permanent-magnet motors Hysteresis motors Reluctance motors Single-phase synchronous motors Direct-current commutator motors Alternating-current commutator motors References & Edit History Related Topics Images Quizzes Energy & Fossil Fuels Electricity: Short Circuits & Direct Currents print Print Please select which sections you would like to print: Table Of Contents CITE verified Cite While every effort has been made to follow citation style rules, there may be some discrepancies. 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External Websites Energy.gov - Determining Electric Motor Load and Efficiency Karlsruhe Institute of Technology - Institute of Electrical Engineering - The invention of the electric motor 1800-1854 MIT OpenCourseWare - Electric Motors The University of Chicago - Department of the Geophysical Sciences - Basics on electric motors UNSW School of Physics Sydney, Australia - Electric motors and Generator Digital Commons at Michigan Tech - Electric Motor and Transmission Integration for Light-Duty Electric Vehicles: A 2023 Benchmarking Perspective and Component Vehicles: A 2023 Benchmarking Perspective and Component Sizing for a Fleet Approach (PDF) Physics LibreTexts - Electric Motor Clemson University Open Textbooks - Science Technology and Society a Student Led Exploration - Electric Motors Edison Tech Center - The Electric Motor three-phase induction motor Cross section of a three-phase induction motor. (more) electric motor Ask Anything Quick Summary Homework Help Written by Gordon R. Slemon Emeritus Professor of Electrical Engineering, University of Toronto. Coauthor of Electric Machines and others. Gordon R. Slemon Fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors Last updated Apr. 24, 2026 • History Britannica AI Ask Anything Quick Summary Table of Contents Table of Contents Quick Summary Ask Anything Top Questions What is an electric motor? How does an electric motor work? What are the main parts of an electric motor? How does electricity make an electric motor spin? What are the different types of electric motors? Where are electric motors used in everyday life? Show more Show less electric motor , any of a class of devices that convert electrical energy to mechanical energy , usually by employing electromagnetic phenomena. Most electric motors develop their mechanical torque by the interaction of conductors carrying current in a direction at right angles to a magnetic field . The various types of electric motor differ in the ways in which the conductors and the field are arranged and also in the control that can be exercised over mechanical output torque , speed, and position. Most of the major kinds are delineated below. Induction motors The simplest type of induction motor is shown in cross section in the figure . A three-phase set of stator windings is inserted in slots in the stator iron. These windings may be connected either in a wye configuration, normally without external connection to the neutral point, or in a delta configuration. The rotor consists of a cylindrical iron core with conductors placed in slots around the surface. In the most usual form, these rotor conductors are connected together at each end of the rotor by a conducting end ring. 1 of 2 waveforms of a three-phase system (more) 2 of 2 production of a rotating magnetic field Production of a rotating magnetic field by three-phase currents in three stator windings. (more) The basis of operation of the induction motor may be developed by first assuming that the stator windings are connected to a three-phase electric supply and that a set of three sinusoidal currents of the form shown in the figure flow in the stator windings. This figure shows the effect of these currents in producing a magnetic field across the air gap of the machine for six instants in a cycle. For simplicity , only the central conductor loop for each phase winding is shown. At the instant t 1 in the figure , the current in phase a is maximum positive, while that in phases b and c is half that value negative. The result is a magnetic field with an approximately sinusoidal distribution around the air gap with a maximum outward value at the top and a maximum inward value at the bottom. At time t 2 in the figure (i.e., one-sixth of a cycle later), the current in phase c is maximum negative, while that in both phase b and phase a is half value positive. The result, as shown for t 2 in the figure , is again a sinusoidally distributed magnetic field but rotated 60° counterclockwise. Examination of the current distribution for t 3 , t 4 , t 5 , and t 6 shows that the magnetic field continues to rotate as time progresses. The field completes one revolution in one cycle of the stator currents. Thus, the combined effect of three equal sinusoidal currents, uniformly displaced in time and flowing in three stator windings uniformly displaced in angular position, is to produce a rotating magnetic field with a constant magnitude and a mechanical angular velocity that depends on the frequency of the electric supply. rotating field and the currents that it produces A rotating field and the currents that it produces in short-circuited rotor conductors. (more) The rotational motion of the magnetic field with respect to the rotor conductors causes a voltage to be induced in each, proportional to the magnitude and the velocity of the field relative to the conductors. Since the rotor conductors are short-circuited together at each end, the effect will be to cause currents to flow in these conductors. In the simplest mode of operation, these currents will be about equal to the induced voltage divided by the conductor resistance. The pattern of rotor currents for the instant t 1 of the figure is shown in this figure . The currents are seen to be approximately sinusoidally distributed around the rotor periphery and to be located so as to produce a counterclockwise torque on the rotor (i.e., a torque in the same direction as the field rotation). This torque acts to accelerate the rotor and to rotate the mechanical load. As the rotational speed of the rotor increases, its speed relative to that of the rotating field decreases. Thus, the induced voltage is reduced, leading to a proportional reduction in rotor conductor current and in torque. The rotor speed reaches a steady value when the torque produced by the rotor currents equals the torque required at that speed by the load with no excess torque available for accelerating the combined inertia of the load and the motor. Britannica Quiz Energy & Fossil Fuels The mechanical output power must be provided by an electrical input power. The original stator currents shown in the figure are just sufficient to produce the rotating magnetic field. To maintain this rotating field in the presence of the rotor currents of the figure , it is necessary that the stator windings carry an additional component of sinusoidal current of such a magnitude and phase as to cancel the effect of the magnetic field that would otherwise be produced by the rotor currents in the figure . The total stator current in each phase winding is then the sum of a sinusoidal component to produce the magnetic field and another sinusoid, leading the first by one-quarter of a cycle, or 90°, to provide the required electrical power. The second, or power, component of the current is in phase with the voltage applied to the stator, while the first, or magnetizing, component lags the applied voltage by a quarter cycle, or 90°. At rated load, this magnetizing component is usually in the range of 0.4 to 0.6 of the magnitude of power component. A majority of three-phase induction motors operate with their stator windings connected directly to a three-phase electric supply of constant voltage and constant frequency. Typical supply voltages range from 230 volts line-to-line for motors of relatively low power (e.g., 0.5 to 50 kilowatts) to about 15 kilovolts line-to-line for high-power motors up to about 10 megawatts. Explore Britannica Premium! The trusted destination for professionals, college students, and lifelong learners. SUBSCRIBE Except for a small voltage drop in the resistance of the stator winding, the supply voltage is matched by the time rate of change of the magnetic flux in the stator of the machine. Thus, with a constant-frequency, constant-voltage supply, the magnitude of the rotating magnetic field is held constant, and the torque is roughly proportional to the power component of the supply current. With the induction motor shown in the foregoing figures, the magnetic field rotates thr